1. Field of the Invention
The present invention relates to a fluid-filled vibration damping device which has a fluid chamber or chambers filled with a non-compressible fluid and which is capable of exhibiting a high damping effect with respect to input vibrations, by controlling the pressure of the fluid within the fluid chamber or chambers and thereby positively utilizing flows of the fluid and a change of the pressure of the fluid.
2. Discussion of the Related Art
As one type of a vibration damper interposed between two members of a vibration system so as to flexibly connect these two members or mount one of these members on the other member in a vibration damping manner, there is known a fluid-filled vibration damping device as disclosed in JP-A-6-294438 (laid-open publication of Japanese Patent Application). Such a fluid-filled vibration damping device includes: a first and a second mounting member which are spaced apart from each other; an elastic body elastically connecting the first and second mounting members; and a movable member which partially defines a primary fluid chamber filled with a non-compressible fluid the pressure of which changes as a result of an elastic deformation of the elastic body upon application of a vibrational load between the first and second mounting members. The movable member is oscillated at a frequency corresponding to a frequency of the input vibrations to be damped by the vibration damping device, whereby the pressure of the fluid in the primary fluid chamber is controlled so as to suitably regulate vibration damping characteristics of the vibration damping device.
As another type of the vibration damper, there is proposed a fluid-filled vibration damping device as disclosed in JP-U-61-191543 (laid-open publication of Japanese Utility Model Application). This type of fluid-filled vibration damping device includes: a first and a second mounting member which are spaced apart from each other; an elastic body elastically connecting the first and second mounting members and partially defining a primary fluid chamber filled with a non-compressible fluid the pressure of which changes upon application of a vibrational load between the first and second mounting members; a movable member which partially defines an auxiliary fluid chamber filled with the non-compressible fluid and which is oscillated to cause a periodic change of a pressure of the fluid in the auxiliary fluid chamber; and means for defining an orifice for fluid communication between the primary and auxiliary fluid chambers. In this type of vibration damping device, the pressure in the auxiliary fluid chamber by the oscillation of the movable member is controlled based on the pressure change which is induced in the primary fluid chamber as a result of elastic deformation of the elastic body upon application of the vibrational load. With the pressure in the auxiliary fluid chamber being controlled, vibration damping characteristics of the vibration damping device can be suitably regulated, based on the flows of the fluid through the orifice or the resonance of the fluid flowing through the orifice, or based on the fluid pressure change which is induced in the primary fluid chamber due to transmission of the pressure change from the auxiliary fluid chamber through the orifice.
In the above-described fluid-filled vibration damping devices, electromagnetic drive means is usually employed for oscillating the movable member. For assuring a high damping effect by controlling the pressure of the fluid in the fluid chamber, it is necessary to oscillate the movable member at an amplitude and a frequency corresponding to those of the input vibrations. To this end, the electromagnetic drive means has to have a sufficiently large drive force for oscillating the movable member, inevitably resulting in an increased size of the electromagnetic drive means including a coil and a permanent magnet, and accordingly an increased size of the entire vibration damping device. That is, the known vibration damping device tends to suffer from difficulty to exhibit a satisfactory damping performance with a required small size thereof.
Further, for assuring a sufficient degree of stability of the electromagnetic force generated by the electromagnetic drive means, the coil, permanent magnet and other components must be built in the damping device with high positional and dimensional accuracy, requiring a high level of skill for the manufacture, complicating the fabrication of the damping device, and accordingly reducing the efficiency of the manufacture of the damping device in a large scale.
Further, the known fluid-filled vibration damping device suffers from other problems such as a temperature rise due to heat generated by energization of the coil, and a relatively large amount of electric power consumption, where the oscillation of the movable member is required to be effected continuously for a long time or with a large drive force, depending upon the specific operating condition or required operating characteristics of the damping device.